Mine roof bolts



Jan. 31, 1967 w. E. WORLEY 3,301,123

MINE ROOF BOLTS Filed March 30, 1.966 5 heets-Sheet 1 INVENTOR: WILLIAME. WORLEY ATTYS.

1A L 2 my #20 7 ///2 L Jan. 31, 1967 -w. E. WORLEY 3,301,123

MINE ROOF BOLTS Filed March so, 1966 5 Sheets-Sheet 2 INVENTOR. WILLIAME. WORLEY #ATTYS.

United States Patent Ofifice 3,31,123 Patented Jan. '31, 1967 3,301,123MINE ROOF BOLTS William E. Worley, 291 Avon Road, Devon, Pa. 19333 FiledMar. 30, 1966, Ser. No. 538,807 11 Claims. (Cl. 85-79) This is acontinuationdn-part application of my prior application Serial No.446,886, filed April 9, 1965, and entitled Mine Roof Bolts, nowabandoned.

The present invention relates to means for supporting roofs of mines andmore particularly to a novel improvement in roof bolts used for thispurpose and the method of making these bolts.

Since the inception of underground mining, the need to support theoverhead ceiling or roof in the underground passageways of a mine hasbeen recognized as essential in order to prevent failure or collapse ofthe roof thereby jeopardizing the lives of men working in theunderground mine. Thus, the problem of safe and adequate roof support isa very serious one. One of the oldest supports employed is use oftimbers or other similar support means such as masonry walls and arches,steel timber sets, metal props, steel and masonry supports and others.These installations are comparatively expensive due to the cost of thesupport materials and mainly the high installation costs. Moreover, thebeam supports are cumbersome and take up valuable space in the mines.Additionally, it has been found that in some instances activity in thestrata or layers above the mine roof sets up forces which the timbersupports cannot withstand and cave-ins result.

A more recent development in this area is the use of elongated roofbolts which are inserted into openings drilled in the strata above theroof of a mine passageway at predetermined spaced apart intervals. Thesebolts are usually three to four feet long and are mounted in verticalholes drilled into the ceiling. These bolts conventionally include sometype of anchor-like fastening means at one end adjacent the uppermostpart of the hole and means at the opposite end of the bolt to place thebolt under tension. By this arrangement it was thought that the strataabove he roof would be compresssed in a vertical direction wherebyseveral thinly bedded bands or strata of rock or other material abovethe roof level would be bound together by means of the bolts to simulatea thicker strata which would be suificiently strong to prevent flexureof the root. In other words, the pattern of roof bolts in the roof wasthought to secure weak roof material to strong massive overlying rocksor to reinforce the immediate roof strata to form a laminated beam.However, in certain situations, for example, where the roof strata doesnot have a solid rock layer for anchorage, this type of bolt has notprovided adequate roof support. An important factor in this regard isthat by compressing the strata vertically, only the tension component ofshear is supported while the compression component is not supported.Further it has been found that if the anchor is located in soft areas ofthe strata above the roof, the anchor slips and the roof starts to sagor bulge in the areas between the bolts and in some cases the entireroof has ultimately failed.

In order to provide opitmum support for the roof strata, it is importantthat the strata supported by the roof bolts be held firmly in place. Ithas been found that comparatively small initial movements of the stratahas a compounding effect which ultimately leads to larger movements ofthe strata and movement of adjacent strata and eventually to completefailure of the roof. Further, it has been found that the presently usedroof bolts do not support the strata in a manner to resist this initialmovement. More specifically it has been observed that anchor slippagewith these prior bolts and bolt elongation by reason of the greatdistance between the anchor and the other terminal end of the boltpermit small movement of the strata which, as noted above, can lead tocomplete failure of the roof.

One prior roof bolt of the type discussed above is known as the slot andwedge bolt. This bolt comprises an elongated rod which has a taperedopening in its upper end to receive a wedge block and is threaded at itslower end. This bolt is installed in a hole in the mine roof by drivingthe wedge block against the top of the hole so that it expands the upperend of the rod into engagement with the side wall of the hole to provideanchor means. A plate is placed over the threaded end of the rod and anut is applied to the threads to tension the bolt. One of theshortcomings of this type of bolt is the fact that it has to be driveninto the hole which could disrupt the mine roof and set up forces whichweaken the roof. Additionally, the hole in the mine roof has to be apredetermined fixed depth and requires a firm top in order to provide astrong surface against which the wedge block engages. Moreover, sincethe anchor end in its expanded condition is of a larger diameter thanthe rod, a considerable amount of space exists betwen the hole and therod throughout its length thereby permitting horizontal or lateralshifting of the strata and thus failing to resist the compressioncomponent of shear stress for a major portion of the bolt. Further, itis clear that this type of bolt is diflicult to remove from the mineroof and is not suitable for reuse.

Another former type of expansion bolt discussed above is the bail-typeexpansion unit. This unit comprises an elongated bolt which is threadedat its inner end and has a head at its other end to accommodate a wrenchfor turning, An internally threaded wedging plug is adapted to bemounted on the threaded end of the bolt and upon downward movement,engages internally of a split sleeve to wedge it outwardly whereby anouter serrated surface of the sleeve grips the wall of the hole andserves as an anchor. In preparing this bolt for installation, a roofplate has to be assembled prior to application of the sleeve and this isusually done at the mine site. After the unit is inserted up into thehole, the head is turned, whereby the tapered plug is threadeddownwardly along the top end of the bolt and spreads the wings or leavesof the sleeve outwardly to engage the wall of the upper portion of thehole. This anchors the bolts at the upper end and continued turining ofthe head places the bolt under tension. As noted above, theory of thistype of support is that a series of these bolts will compress the layersof the material above the roof vertically to compact the roof strata toform a laminated beam. One of the problems with this type of bolt,however, is that the expansion anchor provides a relatively smallcontact area with the wall of the hole, and if the material surroundingthe anchor end is not firm, the sleeve tends to slip and slippage caneventually lead to failure of the roof. Furthermore, small stratamovements produce elongation which also could result in failure of theroof. Moreover, this conventional type of bolt only supports the tensioncomponent of shear stress in the layers above the roof. Furthermore, thebolts are difficult to remove and often are damaged upon removal andthus, are not generally suitable for reuse.

Another prior type of expansion bolt is the type comprising an elongatedrod having a hollow shell portion at its inner end within which iscontained a small explosive charge. This bolt is inserted into a hole inthe mine roof and the small explosive charge is set off to expand theshell into engagement with the wall of the hole at the inner end thereofand serve as an anchor. A hearing plate is then positioned over thelower threaded end of the bolt and a nut is applied to place the boltunder tension. The principle of support of a series of bolts of thistype is the same as that outlined above. In other words, a series ofspaced bolts are designed to compress the roof strata vertically therebycompressing the layers above the roof into the form of a beam. However,it is apparent that if slippage takens place or if the bolt isoverstressed, there is the danger of roof tailure. 'Moreover, it isreadily apparent that this type of bolt is not reusable. Additionally itthe upper portion of the hole is not a solid layer, the anchor will notgrip firmly and slippage is inevitable. Further as is noted above, thistype of support only resists the tension component of shear stress andnot the compression component by reason of the fact that there is only acomparatively small contact area between the anchor sleeve and the wallof the hole.

With the foregoing in mind, the principal object of the presentinvention is to provide a bolt for supporting the roof of mines which ischaracterized by novel features of construction and arrangement toprovide a firm support for the roof and which is highly economical tomanufacture and install. The bolt of the present invention supports theroof strata firmly and resists initial small movements of the stratamuch more effectively than prior bolts by reason of the fact that anchorslippage is practically eliminated and the elfect of bolt elongation islocalized. The bolt of the present invention engages the side wall ofthe hole at a plurality of contact zones throughout the length of thebolt thereby providing a plurality of anchor points as contrasted withthe prior bolts discussed above which have only a small contact with theside wall of the hole at the upper end thereof. Additionally, whereaslocalized strata movement effected elongation of the entire rod in priorbolt constructions, localized strata movements effect small elongationof the bolt of the present invention by reason of the manylongitudinally spaced contact zones. Thus, the effect of the bolt of thepresent invention is to strongly resist strata movement which is themajor cause of roof failure.

The bolt of the present invention comprises broadly a pair of elongatedbars of stepped configuration having confronting, longitudinallyextending faces, each face having a plurality of planar angularlydisposed longitudinally spaced cam surfaces which in the stackedposition of the bolt are in overlying, confronting engagement. Each ofthe "bars has a stepped outer face opposite the cam face provided by aplurality of cutout sections defining a plurality of projections formingcontact points or zones.

One of the elongated bars has a threaded shank depending from one endthereof and the other bar has an axially extending depending sternportion which, when the engaging cam surfaces overlie one another,confronts a portion of the threaded shank. When installing this bolt,the bars which are in a stacked position are inserted up into a hole inthe roof, the hole being of a slightly greater cross section than theopposed contact zones. The bars are now displaced longitudinallyrelative to one another, whereby the opposed contact zones are displacedradially relative to one another clue to the cooperating cam surfaces toengage diametrically opposed areas of the side wall of the hole at aplurality of longitudinally spaced points the entire length of the hole.The bars may be displaced by placing a bearing plate over the threadedshank to engage the lower end of the stem and then applying and turninga nut on to the shank whereby one bar member is drawn downwardly and thecontact points are moved laterally apart to engage the side wall of thehole at a plurality of longitudinally spaced points as shown in FIG. 5of the drawings. By this arrangement, there is a large contact area withthe wall of the hole along the entire length thereof, thus eliminatingthe possibility of slippage of the bolt in the hole. Accordingly, when aseries of spaced bolts is inserted into the roof, the various layers arecompressed laterally whereby the bolts support the compression as wellas the tension component of shear stress in the roof layers. Thus, byessentially filling the hole in the mine roof, lateral movement of thevarious layers of the roof is resisted and a safe roof is provided.Moreover, unlike the prior bolts discussed above, the roof top need notbe solid to firmly anchor the bolt against slippage. Additionally ifthere are projections or irregularities along the side wall of the holeinto which the bolt is inserted, the localized contact areas of the boltexert a great compressive force to crush the projection thereby insuringa good firm anchorage of the bolt in the hole.

The principle of operation of the bolt of the present invention isentirely different from the bolts discussed above and does not rely ontensioning of the bolt as the sole means of support. However, since thebolt of the present invention is vertically oriented and is anchoredessentially throughout its length with the strata of the roof, iteffectively supports the tension components of shear stress as well asthe compression component.

The bolt of the present invention eliminates the need for a separateexpansion device and hence is less costly to make and assemble than someof the prior bolts discussed above. Furthermore, since the bolt can becompletely assembled prior to shipment, there is less handling at themine site and hence it is less costly to install.

Even though it is preferred to make the bolt of the present invention ofsteel, it can be made of a lighter, less corrosive material by reason ofits design.

The bolt of the present invention, in addition to being easy and quickto install, may be easily removed after a period of time and reused andindefinite number of times.

With the foregoing in mind, an object of the present invention is toprovide a roof bolt for use particularly as a support means for mineroots which is characterized by novel features of construction andarrangement providing a firm support for the mine roof.

Another object of the present invention is to provide a roof bolt whichfirmly grips the strata of the roof essentially throughout its length,thus substantially eliminating anchor slippage and minimizing theharmful effect of bolt elongation.

Another object of the present invention is to provide a roof bolt whichpre-stresses the strata or layers of materials above the roof laterallyso that a pattern of these bolts arranged in the mine supports thecompression as well as the tension component of shear stress in the rooflayers.

A further object of the present invention is to provide a bolt which maybe economically and easily manufactured, which is also easy to removeand which can be reused many times.

These and other objects of the present invention and the variousfeatures and details of the construction and use thereof are hereinaftermore fully set forth with reference to the accompanying drawings,wherein:

FIG. 1 shows a section of roof stnata with a bolt in accordance with thepresent invention mounted therein;

FIG. 2 is a view taken on line 22 of FIG. 1 showing a section of theroof with a plurality of bolts in accordance with the present inventioninstalled therein;

FIGS. 3 and 4 are enlarged sectional views taken on lines 33 and 4-4 ofFIG. 1;

FIG. 5 is an enlarged fragmentary view similar to FIG. 1 showing thebolt in the expanded operative position engaging the side wall in thehole in the roof;

FIG. 6 is an enlarged sectional view taken on lines 6-6 of FIG. 5;

FIGS. 7 and 8 are fragmentary perspective views of a bolt in accordancewith the present invention in the stacked and expanded positionsrespectively;

FIG. 9 is a fragmentary perspective view of one of the elements of abolt in accordance with the present invention;

FIG. 10 is a side elevational view of another embodiment of mine roofbolt constructed in accordance with the present invention;

FIGS. 11, 12 and 13 are sectional views of the mine roof bolt assemblyof FIG. taken on lines 1111, 1212 and 13-13 respectively;

FIG. 14 is an enlarged section of a roof strata with the mine roof boltin accordance with the present invention mounted therein;

FIG. 15 is a sectional view through the bolt taken on line 15-15 of FIG.14;

FIG. 16 is a fragmentary exploded perspective view of the bar memberscomprising the second embodiment of bolt;

FIG. 17 is a fragmentary layout of one of the bar members in a stage ofmanufacture;

FIG. 18 is a schematic illustration showing a method for making the barmembers of the mine roof bolt shown in FIG. 10;

FIGS. 19 and 20 are fragmentary views of one of the bar members of themine roof bolt at various stages of manufacture;

FIG. 21 is a view taken on line 2121 of FIG. 20;

FIG. 22 is a sectional view of stock material from from which the otherbar member of the bolt is made;

FIG. 23 is a fragmentary side elevational view of the other bar memberat a stage of manufacture; and

FIG. 24 is a view taken on lines 2424 of FIG. 23.

Referring now to the drawing and particularly to FIG. 1 thereof, thereis shown a typical cross section of the roof of a mine passageway ortunnel which as illustrated is comprised of several strata or layers L.A mine roof bolt 10 in accordance with the present invention is mountedin a vertically extending hole 11 in the roof strata. These bolts areadapted to be inserted in the roof at predetermined spaced apartlocations usually about three to four feet apart as illustrated in FIG.2, and when in the expanded anchored position, the bolts serve topre-stress the strata laterally thereby supporting the compression aswell as the tension component of shear stress in the various layerscomprising the roof, and thereby minimizing flexure and thus, preventingroof failure.

Considering now the specific details of construction, the bolt 10comprises a pair of elongated bar members 12 and 14- having confrontinginterengaging inner faces 13 and 14 respectively. The face 13 is of astepped configuration comprising a plurality of angularly disposed,longitudinally spaced fiat cam surfaces 18 and a plurality of shortradially directed shoulders 19, each shoulder 19 connecting adjacent camsurfaces 18. The face 15 of the bar 14 is also of a steppedconfiguration comprising a plurality of angularly disposed,longitudinally spaced,

fiat planar cam surfaces 20 and a plurality of radially directedshoulders 21 connecting adjacent cam surfaces. The cam surfaces 18 and20 are approximately of equal length so that the bar members nest snuglytogether when in the stacked position shown in FIG. 1 As bestillustrated, the cam surfaces 18 and 20 are disposed at a slight angleto the longitudinal axis of the bar members and the shoulders 19 and 21seat against one another in the stacked position to limit relativelongitudinal movement of the bar members in one direction.

Each bar member as best illustrated in FIGS. 79 inclusive, has a roundedouter side wall opposite the cam face, the outer wall 30 of the bar 12having a plurality of longitudinally spaced cutouts 31 defining aplurality of longitudinally spaced projections which comprise contactzones Z adapted to engage the side Wall of the opening 11. As bestillustrated in FIG. 9, the cutout in the outer side wall is at an anglerelative to a longitudinal axis of the bar member to form a series oftriangularly shaped planar faces 33 approximately parallel to the camsurfaces 18. The bar 14 also has a rounded outer side wall 40 with aplurality of longitudinally spaced cutouts 41 defining longitudinallyspaced projections which comprise contact "zones Z adapted to engage theside wall of the hole or opening 11. These cutouts 41 are also angularlydirected to form a series of triangularly shaped faces 43 approximatelyparallel to the cam surfaces 20. By this arrangement, as bestillustrated in FIG. 1, the contact zones Z and Z are slightly staggeredon either side of a plane transverse to the axis of the bar in thestacked position. In the present instance as illustrated in thedrawings, the spacing between substantially all of the adjacent contactzones is at least equal to the largest cross sectional dimensionmeasured in a plane perpendicular to the longitudinal axis of the boltin the stacked position.

The bar members are adapted for longitudinal movement relative to oneanother between a stacked or closed position (see FIG. 1) and anexpanded position (see FIG. 5). In the stacked position, the maximumcross sectional dimension D of the bolt or the distance between contactzones Z and Z is the smallest to facilitate insertion into the hole 11of a mine roof. In the expanded position (see FIG. 5) the contact zonesZ and Z are displaced laterally due to interengagement of the camsurfaces to a distance apart greater than D. In order to facilitatelongitudinal movement of the bars, the bar member 14 is provided with athreaded shank 50 depending from its lower terminal end which is of across section smaller than the greatest cross section of the bar todefine an abutment shoulder 52 adjacent its lower end. The other barmember 12 has a depending stem 56 which in the stacked position of thebar members (FIG. 7) projects downwardly beyond the shoulder 52. Thelower end of the stem 56 is spaced from the terminal end of the shank 50to expose a portion of the threaded shank thereby to accommodate a plate60 and nut 62.

In the installation of a bolt in accordance with the present invention,the bar members are initially in the stacked position shown in FIGS. 1,3 and 7, wherein the cam surfaces 18 and 20 are in confronting relationfor their entire length and the stem 56 projects downwardly beyond theshoulder 52 of the threaded shank 50. The bar members may be detachablyheld in this stacked position simply by wrapping tape around the barmembers at selected locations along their length. The bolt in itsstacked position is then inserted up into the opening 11 in the mineroof, the opening being of a slightly greater cros sectional dimensionthan the greatest cross section D of the bolt in its stacked position toprovide a very small clearance therebetween. For example, for an opening11 having a diameter of about 1.375 in., the distance D between thecontact zones Z and Z of the bar members is approximately 1.250 in.Thereafter, the bearing plate 60 is positioned over the threaded shank50 and the nut 62 is threaded on the shank 50. Now, as the nut 62 istightened against the bearing plate 60, the bar member 14 is displacedlongitudinally downwardly relative to the bar member 12. Relativelongitudinal displacement of bar members causes relative lateraldisplacement of contact points or zones Z and Z due to the interactionof the cam surfaces 18 and 20 whereby the side wall of the opening 11 isengaged at a plurality of longitudinally spaced points along the lengththereof as best illustrated in FIG. 5. By this arrangement, when aseries of bolts is installed n the roof at their predetermined spacedapart locations 1n the manner shown in FIG. 2, the layers L of the roofstrata are prestressed in a lateral direction for a substantial heightabove the roof level whereby the compression and the tension componentsof shear stress in the layers or strata L are supported. In this mannera firm support is provided. Now, when it is desired to remove the bolts,the nut 62 is simply threaded off the shank 50, the plate 60 is removedand then merely by tapping the free terminal end of the shank 50upwardly, the bar members are urged to a stacked position whereby theymay be easily removed from the opening in the roof.

The roof bolts of the present invention may be made relativelyeconomically. For example, the bolt may be made by die stamping, forgingor rolling.

There is shown in FIGS. 10-17 another embodiment of mine roof bolt 100in accordance with the present invention. The specific details andconstruction of the bolt are best illustrated in FIGS. 10, 14 and 16,and as illustrated therein, the bolt 100 comprises a pair of elongatedbar members 102 and 104 having confronting interengaging inner faces orsurfaces 106 and 108 respectively of a predetermined configurationwhereby upon relative axial displacement of the bar members, the membersmay be actuated from a stacked position (see FIG. 10) for insertion intoa hole or opening 110 in the roof strata to an expanded position (seeFIG. 14) wherein the opposing outer surfaces of the members aredisplaced laterally into pressure-applying relation with the side wallof the opening 110 in the roof strata.

To this end, the bar member 102 which may be of halfmoon cross sectionand of a serpentine shape, has an inner surface or face 106 of steppedconfiguration comprising a plurality of angularly disposedlongitudinally spaced planar or flat cam surfaces 112, each cam surface1112 ten minating in a rounded edge and merging with a plurality ofshort angularly directed shoulders 114, each shoulder connectingadjacent cam surfaces 112. The outer surface or face 117 of the barmember 102 is also of a stepped configuration defining a plurality oflongitudinally spaced projections defining contact zones Z adapted toengage the side wall of the opening 110 in the roof strata at aplurality of spaced locations. In the present instance as illustrated inthe drawings, the spacing between substantially all of the adjacentcontact zones Z is at least equal to the largest cross sectionaldimension measured in a plane perpendicular to the longitudinal axi ofthe bolt in the stacked position.

The bar member 104, in the present instance, is an elongated hollowmember of generally U-shaped cross section having longitudinal spacedapart side edges 117a and 11712 of a stepped configuration to define aplurality of angularly disposed, longitudinally spaced flat cam surfaces120 and a plurality of short, angularly directed shoulders 122, eachshoulder merging with adjacent cam surfaces 120 in a rounded edge andconnecting adjacent cam surfaces 120. In the present instance, the outerface of the bar member 104 is a continuous surface defining onecontinuous contact zone Z extending the length of the bar member 104.The cam surfaces 112 and 120 of the bar members are approximately ofequal length so that the 'bar members nest snugly together when in thestacked position shown in FIG. 10. As illustrated, the cam surfaces 112and 120 are disposed at a slight angle to the longitudinal axis of thebolt and the shoulders 114 and 122 seat against one another in thestacked position to limit relative longitudinal movement of the barmembers in one direction.

The bar members are adapted for relative longitudinal movement between astacked or closed position and an expanded position and in the stackedposition the maximum cross sectional dimension D of the bolt or thedistance between the contact zones Z and Z at any point along the lengthof the bolt is smaller to facilitate insertion into the hole 110 of theroof strata. In the expanded position, the contact zones are displacedlaterally due to interengagement of the cam surfaces to a distance apartgreater than D. The means for eifecting longitudinal movement of thebars includes, in the present instance, a threaded shank 127 dependingfrom the lower terminal end of the bar member 104 which is of a crosssection smaller than the outer cross section of the bar member to definean abutment shoulder 129 adjacent its lower end. The bar member 102 has21 depending stem 130 which in the stacked position of the bar membersprojects downwardly beyond the shoulder 129 so that its lower end isspaced from the terminal end of the shank to expose a portion of thethreaded shank 127 to accommodate a plate 132 and nut 134.

In the installation of bolt of the type described above, the bar members102 and 104 are initially in the stacked position shown in FIG. 10,being held in that position by means of strips of tape 135 atlongitudinally spaced points. It is noted that the bolt is delivered tothe mine site in this condition thereby obviating the need for anytime-consuming assembly operation. Furthermore, the assembly iscomparatively light thereby facilitating handling in the mines. In itsstacked position, the bolt is then inserted up into the opening in themine roof, the opening 110 being of a slightly greater cross sectionaldimension than the greatest cross section D between the contact zones Zand Z With the bolt so positioned, the nut 134 is turned to effectrelative longitudinal displacement of the bar members. This longitudinaldisplacement effects lateral displacement of the contact zones Z and Zdue to the interaction of the cam surfaces 112 and whereby the side wallof the opening is engaged at a plurality of longitudinally spaced pointsof the bar member 102 and the contact zone Z of the other bar member 104engages the side wall of the other opening along its entire length. Bythis arrangement, when a series of bolts is installed in the roof at aplurality of predetermined spaced apart locations, the layers of theroof strata are pre-stressed in a lateral direction for a substantialheight above the roof level whereby the compression and tensioncomponents of shear stress in the layers are supported. It is noted thatthis bolt arrangement provides for a large gripping area. Furthermore,bolt elongated is minimized due to the continuous area of contactbetween the bolt and the wall of the hole. Thus, forces developingbetween adjacent layers of strata are supported by a relatively shortlength of bolt and elastic elongation is therefore minimal. The boltsmay be removed from the mine when desired simply by threading down thenut 134 and tapping the free terminal end of the shank 127 whereby thebars are urged to a stacked position. It is noted that if an elastictape is used, the tape retains the bar members in the stacked positionwhen removed from the roof to facilitate reuse. The specificconfiguration of the mine roof bolt shown in FIGS. 10-17 inclusive andmore particularly the provision of the tubular bar member 104 minimizesthe possibility of flattening out of the confronting cam surfacesaccordian-style which would tend to reduce the effective gripping forceof the mine roof bolt when assembled in an opening in the roof of amine. This construction also minimizes bolt elongation, which, as notedabove, is an important factor contributing to failure of the roof.

Another feature of the present invention is the provision of a simpleand economical means for manufacturing a mine roof bolt of the typeillustrated in FIGS. l0 16. In accordance with the present invention,the bar member 104 may be formed by bending an elongated flat striphaving a predetermined, irregular side edge configuration to a generallycircular shape so that the side edge portion define the cam surface andshoulders. In the preferred method of the present invention the barmemher 104 may be formed from fiat sheet stock by cutting the sheet intoa plurality of strips having the desired edge configuration to definethe cam surfaces and shoulders. Thereafter, each individual flat stripis formed, for example, by a rolling process to the U-shapedconfiguration as shown in FIG. 16, the continuous rolled strip thenbeing cut to size by suitable means. The other bar memher 102 may beformed from a continuous piece of bar stock having a half-moon crosssection by a bending operation in a joggle mill or the like to definethe configuration shown having the series of adjacent angularly disposedcam surfaces. This zig-zag or serpentine piece of bar stock is thensuitably cut to size and assembled to the other bar member and heldthereto by means, for example, of a series of adhesive strips. The boltis now ready for use. It is noted that, as mentioned above, the adhesivemay be a flexible type so that when the bolt is used in a mine roof, theadhesive does not sever and remains in place when the bolt should beremoved from the hole in the mine roof for reuse.

There is illustrated schematically in FIG. 18 a method for making andassembling a mine roof bolt in accordance with the present invention. Asillustrated therein, there are two separate assembly lines A and B formaking the respective bar members 104 and 102 of the roof bolt. In lineA, fiat sheet stock 150 is fed to a cutting device 152 such as a torchcutting apparatus or a plurality of cooperating disc-like cutting knivesto cut the sheet 150 longitudinally into a plurality of side by sidestrips 154 having a serpentine or corrugated side edge configuration todefine the cam surfaces 120 and connecting shoulders 122 when the stripis rolled. The strips 154 are then taken up on a plurality of take-uprolls at a storage or recoiler station 156, the roll assembly beingmounted on trackways so that a selected roll may be positioned inregistry with the remainder of the stations in line A. It is noted thatthe direction of feed from the storage rolls for alternate strips has tobe reversed for proper orientation at a later time at the assemblystation with the other bar member.

As a strip 154 is wound from the storage roll, it passes through anuncoiling device 158 and a leveler 160 to a prenotch press 162, where,as illustrated in FIG. 19, the strip 154 is out part way throughtransversely to its axis at predetermined spaced apart intervals whichdefine the length of the bar. The strip 154 is then formed into acircular cross section of generally U-shaped configuration in a rollforming mill 164 and from there, the rolled up strip 154 passes throughthe cutoff press 166 where the rolled up strip is severed at theprenotched points to form the bar member 104. The threaded stud 127 isthen assembled to each of the individual bar members 104 at an automaticwelding station 170.

The bar member 102 of the bolt is formed on line B in FIG. 18 and asillustrated therein a continuous piece of stock 172 of half-moon crosssection is fed through an uncoiler 174 to a leveler 176 and then is fedinto a joggle mill 178. In the joggle mill 178, the fiat bar stock 172is deformed by suitable means to the serpentine configurationillustrated in FIG. 18. The so deformed bar leaves the joggle mill andpasses through a cutoff press 180 where the bar is cut into suitablelengths and one end of the bar is straightened out to define the stem.The completed bar is then transferred to the automatic assemblingstation 182 where it is mated with a bar 104 and the tape 135 is appliedat preselected points so that the finished assembly is ready for use.

From the above, it is readily apparent that the present inventionprovides a comparatively simple and highly economical method formanufacturing mine roof bolts. By the method of the present inventionthere is comparatively little waste since no machining operations arerequired to produce the bolt. Further, substantially all of themanufacturing and assembly operations may be carried out on automaticequipment thereby reducing labor costs. Even though the preferredmaterial for making the bolt is steel, other materials such asfiberglass reinforced plastic may be used.

While the bolt of the present invention is primarily used in mines forsupporting the roof of the mine, it is to be understood that it may beused effectively in other underground passageways to support theoverlying strata. Additionally, the bolt has other useful applications,for example, in certain road excavation operations the bolt may be usedto prevent rock slides.

While particular embodiments of the present invention have beenillustrated and described herein, it is not intended to limit theinvention and changes and modifications may be made therein within thescope of the following claims. For example, the coefficient of frictionbetween one or both the bar members and the wall of the opening in themine roof may be increased by roughening the surfaces of the bar membersconfronting and engaging the wall of the hole, for example, by knurling,ridging or other suitable roughening means. Additionally, the internalfriction between the confronting cam surfaces of the bar members may bereduced by suitable permanently applied lubricant means to the camsurfaces.

1 claim:

1. A bolt adapted to be mounted in in elongated opening in the roof of amine comprising a pair of elongated bar members, the inner surface ofone of said bar members having a plurality of spaced angularly disposedcam= surfaces, lt-he other bar member being of generally U-shaped crosssection and having longitudinal, spaced apart side edges of steppedconfiguration to define a plurality of longitudinally spaced camsurfaces angularly disposed in the same direction as the cam surfaces ofsaid one bar member, means for effecting longitudinal displacement ofsaid bar members between a stacked position wherein the bar members arenested together and an expanded position whereby the outer side walls ofthe bar members opposite said cam surface are displaced laterally intopressure-applying relation with the side wall of the opening, the outersurface of said one bar member having a plurality of longitudinallyspaced projections defining a plurality of longitudinally spaced contactzones adapted to engage the side wall of the opening upon displacementof the bar members to the expanded position, the spacing betweensubstantially all of the adjacent contact zones being at least equal tothe largest cross sectional dimension measured in a plane perpendicularto the longitudinal axis of the bolt in the stacked position.

A mine roof bolt as claimed in claim 1 wherein said one bar member is ofhalf-moon cross section and of serpentine shape having an inner surfaceof stepped configuration comprising a plurality of angularly disposedlongitudinally spaced planar cam surfaces, each of said cam surfacesterminating in a rounded edge and merging with a plurality of angularlydirected shoulders, said shoulders connecting adjacent cam surfaces andwherein the outer surface of said one bar member is also of steppedconfiguration defining a plurality of longitudinally spaced projectionsdefining contact zones adapted to engage the side wall of the openingupon displacement of said bar members to the expanded position.

3. A mine roof bolt as claimed in claim 1 wherein the side edges of saidother bar member include a plurality of an gurlarly disposedlongitudinally spaced flat cam surfaces and a plurality of shortangularly directed shoulders merging with adjacent cam surfaces in arounded edge and connecting adjacent cam surfaces.

4. A mine roof bolt as claimed in claim 1 wherein one bar member has alongitudinally directed stem projecting from one end thereof and theother bar member has a longitudinally directed threaded shank projectingfrom one end thereof, and including internal-1y threaded means mountedon said shank to engage said stem to effect longitudinal relativemovement of said bar members.

. 5. A bolt adapted to be mounted in an elongated openmg in the roof ofthe mine comprising a pair of elongated bar members having confrontinglongitudinally extending faces, the face of one of said bar membersbeing of a stepped configuration and comprising a plurality oflongitudinally spaced angularly disposed cam surfaces, adjacent camsurfaces being connected by fiat shoulders extending transverse to thelongitudinal plane of the bar members, the other of said bar membersbeing also of a stepped configuration and comprising a plurality oflongitudinally spaced angularly disposed cam surfaces, adjacent camsurfaces of said other bar member being connected by flat shouldersextending transversely to the longitudinal plane of the bar member, eachbar member having a side wall opposite the cam face having a pluralityof longitudinally spaced projections defining contact zones, means foreffecting longitudinal displacement of said bar members "between astacked position wherein the cam sun-faces are confronting andcoextensive and the distance between 1 1 opposed contact zones isminimum and of a smaller dimension than the cross section of the openingto permit the bolt to he inserted into the opening and a stackedposition whereby the cam surfaces cooperate to effect lateraldisplacement of the bar members and engagement of the respective contactzones with the side wall of the opening thereby to engage the opening ata plurality of longitudinally spaced points along the entire lengththereof, the spacing between substantially all of the adjacent contactzones being at least equal to the largest cross sectional dimensionmeasured in a plane perpendicular to the longitudinal axis of the boltin the stacked position.

6. A mine roof bolt as claimed in claim 5 wherein the contact zones aredefined by a plurality of cutouts in the side Wall of the bar memberswhich extend at an angle relative to the longitudinal axis of the bar toform series of triangularly shaped planar faces approximately parallelto the cam surfaces.

7. A mine roof bolt as claimed in claim 5 wherein the outer side Wall isrounded.

'8. A 'bolt adapted to be mounted in an elongated opening in the roof ofa mine comprising a pair of elongated bar members having innerconfronting longitudinally extending surfaces, the inner surface of eachof said bar members having a plurality of longitudinally spaced camsurfaces which are angularly disposed in the same direction, adjacentcam surfaces being connected by shoulders, means for effecting relativelongitudinal displacement of said bar members from a stacked positionwherein the hat members are nested together and an expanded positionwhereby the outer surfaces of the bar members opposite said cam surfacesare displaced laterally into pressure applying relation with the sidewall of the opening and means defining a plurality of longitudinallyspaced projections on the outer face of at least one of said bar membersproviding a plurality of longitudinally spaced contact zones adapted toengage the side wall of the opening upon displacement of the bar membersto an expanded position, the spacing between substantially all of theadjacent contact zones being at least equal to the largest crosssectional dimension measured in a plane perpendicular to thelongitudinal axis of the bolt in the stacked position.

9. A bolt as claimed in claim 8 wherein both of said bar members are ofhalf-moon cross section and wherein the outer surface of each bar memberis of stepped configuration to define a plurality of longitudinallyspaced projections providing longitudinally spaced contact zones.

10. A mine roof bolt as claimed in claim 8 wherein one bar member has alongitudinally directed stem projecting from one end thereof and theother bar member has a longitudinally directed threaded shank projectingfrom one end thereof, and including internally threaded means mounted onsaid shank to engage said stem to effect longitudinal relative movementof said bar members.

H. A mine roof bolt as claimed in claim 8 wherein at least one of saidbar members is of half-moon cross section and wherein the outer surfaceof said one bar member is of a stepped configuration to define aplurality of longitu-dina-lly spaced projections providing a pluralityof longitudinally spaced contact zones adapted to engage the side Wallof the opening upon movement of said bar members to the expandedposition.

References Cited by the Examiner UNITED STATES PATENTS 1,864,300 6/1932Forrest -79 2,878,709 3/ 1959 Horvath 85--87 3,232,163 2/ 1966 Croessant8583 FOREIGN PATENTS 711,324 6/ 1954 Great Britain.

CARL W. TOMLIN, Primary Examiner.

R. S. BRITTS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,301,123 January 31, 1967 William E. Worley It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 1, line 42, for "he" read the column 2, line 46, for "turining"read turning column 3, line 5, for "takens" read takes column 4, line31, for "and", second occurrence, read an column 5, line 23, strike out"from"; line 64, for "outer" read outer side column 10, line 7, for"in", second occurrence, read an column 11, line 3, for "stacked" readexpanded Signed and sealed this 17th day of October 1967.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissionerof Patents

1. A BOLT ADAPTED TO BE MOUNTED IN IN ELONGATED OPENING IN THE ROOF OF AMINE COMPRISING A PAIR OF ELONGATED BAR MEMBERS, THE INNER SURFACE OFONE OF SAID BAR MEMBERS HAVING A PLURALITY OF SPACED ANGULARLY DISPOSEDCAM SURFACES, THE OTHER BAR MEMBER BEING OF GENERALLY U-SHAPED CROSSSECTION AND HAVING LONGITUDINAL, SPACED APART SIDE EDGES OF STEPPEDCONFIGURATION TO DEFINE A PLURALITY OF LONGITUDINALLY SPACED CAMSURFACES ANGULARLY DISPOSED IN THE SAME DIRECTION AS THE CAM SURFACES OFSAID ONE BAR MEMBER, MEANS FOR EFFECTING LONGITUDINAL DISPLACEMENT OFSAID BAR MEMBERS BETWEEN A STACKED POSITION WHEREIN THE BAR MEMBERS ARENESTED TOGETHER AND AN EXPANDED POSITION WHEREBY THE OUTER SIDE WALLS OFTHE BAR MEMBERS OPPOSITE SAID CAM SURFACE ARE DISPLACED LATERALLY INTOPRESSURE-APPLYING RELATION WITH THE SIDE WALL OF THE OPENING, THE OUTERSURFACE OF SAID ONE BAR MEMBER HAVING A PLURALITY OF LONGITUDINALLYSPACED PROJECTIONS DEFINING A PLURALITY OF LONGITUDINALLY SPACED CONTACTZONES ADAPTED TO ENGAGE THE SIDE WALL OF THE OPENING UPON DISPLACEMENTOF THE BAR MEMBERS TO THE EXPANDED POSITION, THE SPACING BETWEENSUBSTANTIALLY ALL OF THE ADJACENT CONTACT ZONES BEING AT LEAST EQUAL TOTHE LARGEST CROSS SECTIONAL DIMENSION MEASURED IN A PLANE PERPENDICULARTO THE LONGITUDINAL AXIS OF THE BOLT IN THE STACKED POSITION.